Lee
Townsend, Extension Entomologist
Department of Entomology
University of Kentucky College of Agriculture

The next 3 weeks is a critical period
in terms of minimizing exposure of pregnant mares to Eastern Tent Caterpillar
(ETC) larvae. The caterpillars are still aggregated on trees and are at their
most vulnerable stage in terms of control. While the overall ETC population
is greatly reduced compared to recent years, there are some pockets where tents
are relatively abundant.

ETC
larvae are present in a wide range of sizes now. Some of the earliest hatched
caterpillars are over an inch long while those from eggs that were among the
last to hatch are in the one-half inch range. Many smaller groups of caterpillars
from individual egg masses have moved to join other colonies on the tree in
larger tents near or on the trunk. These are enlarging significantly as the
accumulated caterpillars grow and continue to add layers of silk.

Most caterpillars now exceed
the size range in which they are most susceptible to Bt-based sprays and it
is nearing the end of the optimum timing window for tree injection. Accessible
nests can be destroyed or treated with a pyrethroid spray.

ETC should remain on the trees for
about two weeks and will continue to feed until mature. They are unlikely to
abandon their current site as long as there is enough foliage to support them
and they are not ready to pupate. In previous years early movement of caterpillars
occurred as they defoliated their home trees and were forced to move (about
May 1). This would be about the time to check locally high populations so that
control could be initiated before they disperse. In most instances this season
ETC numbers are not great enough to defoliate moderate to large trees. They
should remain in place and leave their trees to find pupation sites in about
2 weeks. Last year ETC cocoons were being spun about May 10.